The aim of undertaken studies was to determine the effect of differentiated nitrogen fertilization and the developmental phase of maize on the respiration and dehydrogenases activity under maize cropped for CCM. The experiment was carried out in Experimental and Didactic Unit Złotniki belonging to Poznań University of Life Sciences. The studies were carried out in the years 2007-2009. Soil samples for analyses were taken on six sampling occasions during the vegetation season: before sowing, in the phase of 2-3 leaves, in the phase of 7-8 leaves, in the phase of tasseling, in the milk maturity stage and after harvest. Thalmann’s method was used to determine dehydrogenases activity and the soil respiration activity was determined with the use of titration method. Significant effect was found on differentiated nitrogen fertilization and the developmental phase of maize on the dehydrogenases and respiration activity in the soil.